Funds are requested for the purchase of a high-mass, high-resolution tandem mass spectrometer. The mass spectrometer will be a modified version of a commercially available BEQQ instrument. The modifications include an octapole (o) instead of a quadrupole (q), features for perfomting photodissociation experiments, and features for perfomiing fundamental studies in the gas-phase chemistry of large biomolecular ions. The instrument will be housed in the Chemistiy Department in the interest of eff-icient operation and maintenance of the instrument. The current research of eleven NIH-funded investigators will be enhanced by this instrument. Furthermore, six other NIH-funded investigators have expressed a strong interest in the use of the instrumentation in five years. An association with the Emory Nhcrochemistry Center, originally funded by NIK also may provide an indirect use of the instrument to researchers outside the University community. Researchers who will use the proposed instrument are all performing biomedical-oriented research in diverse fields that require structure elucidation of neuropeptides in CNS, phosphoseryl peptides, bioactive peptide hormones, unknown sphingoid bases, phospholipids, uremic growth inhibitors, enzymes involved in neurohormone synthesis, flavoenzymes, and the anion exchange membrane protein band 3. Others are involved in studying the metabolism of glutathione, effects of ionizing radiation on DNA, and the structure and function of the enzyme myeloperoxidase. Other research involves investigating intrinsic interactions between metal ions and biological ligands, interactions between drugs and proteins and between host and guest molecules, energetics of fragmentations of biomolecular ions, and the fundamental photochemistry that is associated with the acdon of some anti-AIDS compounds. The proposed instrument is essential to the goals of these research projects.